This invention relates to sheet feeding apparatus using an elastic body at its power transmission portion, and particularly to a sheet feeding servo apparatus requiring precise control of the position and speed of a sheet as does an apparatus for reading information from the sheet and writing it thereon while the sheet is being fed.
In the conventional sheet feeding apparatus, the shaft of the actuator for generating power is often not directly coupled to the sheet feeding shaft for feeding the sheet but is coupled thereto through a power transmission mechanism of which the type varies, for convenience of speed change and mounting. An example thereof is disclosed in Japanese Patent Application Laid-Open No. 78212/1979. This power transmission mechanism includes gear, belt, chain and so on. Use of belt will result in great influence on the characteristics of the sheet feeding apparatus because power is transmitted through the elastic belt. When a slender shaft is used for transmission of power, it acts as an elastic body to reduce its torsional rigidity. As a result, the dynamic characteristics of the sheet feeding apparatus is greatly influenced similarly as in the above description. That is, in the sheet feeding apparatus of this kind, the actuator for generating power is provided with an encoder for detecting the position signal thereof, and the position signal detected by the encoder is fed back to the input of the actuator by a position servo system thus to control the position. However, for rapid acceleration, the sheet cannot be controlled precisely.